1. Field of the Invention
This invention relates to optical measuring devices, and more particularly, it is concerned with improvements in an optical measuring device suitable for use in an optical measuring device for measuring dimensions of a workpiece being measured through the utilization of uneasily visible or invisible laser beams, comprising a parallel scanning ray beam generator, condensing means for condensing parallel scanning ray beams after the parallel scanning ray beams have passed through the workpiece being measured, and a single light receiving element for sensing the brightness of the scanning ray beams condensed by the condensing means to convert the same into an electric signal, whereby the dimensions of the workpiece being measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece being measured, which has been interposed between the parallel scanning ray beam generator and the light receiving element.
2. Description of the Prior Art
Heretofore, there has been known a high speed scanning type laser length measuring instrument wherein rotary scanning ray beams (laser beams) are converted by a collimator lens into parallel scanning ray beams being passed through a space between this collimator lens and a condensing lens, a workpiece being measured is interposed between the collimator lens and the condensing lens, and the dimensions of the workpiece being measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by this workpiece being measured.
As shown in FIG. 1, the length measuring instrument is constructed such that laser beams 12 are oscillated from a laser beam source 10 toward a stationary mirror 14, the laser beams 12 thus reflected by this stationary mirror 14 are converted by a rotary mirror 16 into scanning beams 17, the scanning beams 17 are converted by a collimator lens 18 into parallel scanning ray beams 20, a workpiece being measured 24, which has been interposed between the collimator lens 18 and the condensing lens 22, is scanned at high speed by the scanning ray beams 20, and the dimensions of the workpiece being measured 24 in the scanning direction are measured from the time length of a dark portion or bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece being measured 24 at that time. More specifically, the dark and bright portions of the parallel scanning ray beams 20 are detected as variations in output voltage of a light receiving element 26 disposed at the focal point of the condensing lens 22, signals from the light receiving element 26 are supplied to a pre-amplifier 28, where the signals are amplified, and thereafter, the signals thus amplified are supplied to a segment selector circuit 30. To measure the time length of the dark portion or the bright portion corresponding to a measuring segment, this segment selector circuit 30 time-shears the output from the light receiving element 26, generates a voltage V to open a gate circuit 32 only for a time t, during which the measuring segment of the workpiece being measured 24 is being scanned, and supplies the same to the gate circuit 32. This gate circuit 32 is supplied with clock pulse CP from a clock pulse oscillator 34, whereby the gate circuit 32 inputs to a counting circuit 36 a clock pulse P corresponding to a time t in accordance with the dimensions of the measuring segment of the workpiece being measured 24. The counting circuit 36, counting the clock pulse P, outputs a counted signal to a digital indicator 38, which digitally indicates the dimensions of the measuring segment of the workpiece being measured 24. Meanwhile, the aforesaid rotary mirror 16 is rotated in synchronism with the clock pulse CP outputted from the clock pulse oscillator 34 by a synchronous sine-wave generator 40 for generating sine waves in synchronism with an output from the clock pulse oscillator 34 and a synchronous motor 44 driven in synchronism with an output from a power amplifier 42, so that the accuracy in measuring can be maintained.
The high-speed scanning type laser length measuring instruments of the type described, because of being capable of measuring the lengths, thickness and the like of moving workpieces and workpieces heated to a high temperature at high accuracy in non-contact relationship therewith, have been widely utilized. However, in general, since a helium-neon laser is used as the aforesaid laser beam source 10, the parallel scanning ray beams 20 become uneasily visible light beams, whereby it has extremely difficult to dispose the workpiece to be measured 24 in portion within the scanning scope of the parallel scanning ray beams 20 or to ascertain whether the workpiece 24 thus disposed is located at the optimum position within the scanning scope. In consequence, as indicated by a broken line in the aforesaid FIG. 1, heretofore, an object of projection 46 such as a piece of paper or a fluorescent screen is interposed between the workpiece being measured 24 and the condensing lens 22 in the light path of the parallel scanning ray beams 20, and judgment is made whether the position of the workpiece being measured 24 is suitable or not from the positions of the parallel scanning ray beams on the object of projection 46. However, with the method of this type using the object of projection 46, it takes much time to ascertain the positions, and moreover, when the object of projection 46 is inserted in the light path of the parallel scanning ray beams 20 in order to ascertain the position of the workpiece being measured 24, it is impossible to simultaneously measure the dimensions of the workpiece being measured 24. Furthermore, it is dangerous to visually ascertain the positions of the parallel scanning ray beams 20 on the object of projection 46, when the output from the laser beam source 10 is large. Further, when a semiconductor laser is used as the laser beam source 10, the parallel scanning ray beams 20 become invisible rays, and hence, it has been disadvantageous in that it is impossible to ascertain the positions of the parallel scanning ray beam 20 on the object of projection 46 even when the object of projection 46 is used.
Meanwhile, it is conceivable to provide an analog monitor meter to indicate the center position of the measuring segment of the workpiece being measured 24 within the scanning scope of the parallel scanning ray beams 20. However, when there are two or more measuring segments of the workpiece being measured 24 or a portion of the workpiece being measured 24 projects out of the scanning scope of the parallel scanning ray beams 20, it is impossible to obtain the center portion of the workpiece being measured 24, thus presenting the disadvantage that no suitable indication of the position can be provided by the analog meter.